This invention generally relates to the art of electrical circuitry and, particularly, to a method of fabricating a laminated circuit assembly, such as an assembly for adhering to the face of a control panel of an electrical appliance.
Laminated circuit assemblies are used in a wide variety of applications. For instance, such circuit assemblies are used in laminated electrical switches which sometimes are called membrane or xe2x80x9ctouchxe2x80x9d switches. A membrane switch may include an insulative substrate or circuit sheet, such as of plastic material, which mounts or supports thin conductive contacts, such as printed circuitry. A flexible membrane is laminated to the substrate. In a normally open membrane switch, a spacer layer often is sandwiched between the membrane and the substrate, with an aperture in the spacer layer aligned with the contacts. When the flexible membrane is depressed in the area of the aperture in the spacer layer, it flexes such that a contact on the membrane engages the contacts on the substrate to close the switch.
Laminated circuit assemblies, such as laminated electrical switches as described above, often are adhered to the face of a control panel of an electrical appliance, such as household appliances. In these applications, the back side of a substrate or circuit sheet has an adhesive film applied thereto, and a flexible backing sheet is adhered to the adhesive. When it is desired to apply the circuit or switch assembly to the face of the control panel of the electrical appliance, the backing sheet is stripped from the substrate to expose the adhesive on the back side of the substrate. In order to facilitate stripping the backing sheet, a pull tab is formed out of the substrate and remains adhered to the flexible backing sheet so that the backing sheet can be easily grasped and stripped. Problems often are encountered in forming the pull tab from the substrate so that the pull tab is easily separated from the substrate to facilitate stripping the flexible backing sheet.
In particular, the various sheets or layers of the laminated circuit assembly are cut to their desired shapes or configurations in stamping-type cutting operations. In order to be able to separate the pull tab from the remainder of the substrate or circuit sheet, a cut or slit must be stamped which will define and separate the pull tab from the substrate. This cut must not cut through the backing sheet or else the pull tab would separate from the backing sheet when pulled, rendering the pull tab useless for the purpose of stripping the backing sheet from the substrate. Positioning the cutting blade such that it will reliably cut completely through the substrate but not through the backing sheet is very difficult. This difficulty can result in the production of many assemblies that are out of specification, thereby increasing scrap cost. The present invention is directed to solving these problems.
An object, therefore, of the invention is to provide a new and improved method of fabricating a laminated circuit assembly of the character described.
Another object of the invention is to provide a method of fabricating a laminated circuit assembly for adhering to the face of a control panel of an electrical appliance, for instance.
In the exemplary embodiment of the invention, the method includes the steps of providing a plastic circuit sheet with electrical circuitry printed thereon. A slit is cut in the circuit sheet in an area where a pull tab subsequently is to be located. An adhesive is deposited on a back side of the circuit sheet, and a backing sheet is adhered thereto. The resulting laminated circuit sheet and backing sheet are cut with a peripheral cut around the circuitry. The peripheral cut intersects the slit with the cut forming a pull tab projecting outwardly from the slit. Therefore, the pull tab can be grasped and separated from the circuit sheet to strip the backing sheet from the circuit sheet when it is desired to adhere the circuit sheet to the face of the control panel.
The slit is preferably U-shaped with the side legs of the U-shaped configuration defining spaced slit portions. The peripheral cut intersects the side legs of the U-shaped slit. The U-shaped slit is cut so that the side legs of the U-shaped configuration project outwardly.
As disclosed herein, the backing sheet is provided of flexible material. The circuit sheet is of a material more rigid or stiff than the backing sheet. The invention is disclosed herein in a laminated electrical switch which includes a switch sheet adhered to the front side of the circuit sheet. A spacer layer is positioned between the switch sheet and the circuit sheet.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.